The Distributive Property of Equality is not a valid justification for the proof.
The correct answer to the given question is option D.
The incorrect justification for the proof is the Distributive Property of Equality.
Substitution is a valid justification when replacing variables with statements, as long as those statements are true.
The Addition Property of Equality states that if two quantities are equal, adding the same value to both sides of the equation will preserve the equality.
The Transitive Property of Equality states that if two quantities are equal to a third quantity, then they are equal to each other.